Nematic liquid-crystalline phases

ABSTRACT

The invention relates to the use of trifluorotoluene derivatives of the formula I ##STR1## in which R 1  is alkyl having 1 to 12 carbon atoms in which, in addition, one or more non-neighboring CH 2  groups may be replaced by --O--, --CO--, --O--CO--, --CO--O--, --O--CO--O--, --CH-halogen, --CH--CN-and/or --CH=CH--, 
     A 1  and A 2 , in each case independently of one another, are 1,4-phenylene in which, in addition, one or more CH groups may be replaced by N, trans-1,4-cyclohexylene in which, in addition, one or two non-neighboring CH 2  groups may be replaced by --O--and/or --S--, or 1,4-bicyclo(2,2,2)octylene, each of which is unsubstituted or monosubstituted or poly-substituted by halogen, nitrile and/or CH 3 , 
     Z 1  and Z 2 , in each case independently of one another, are --CO--O--, --O--CO--, --CH 2  O--, --OCH 2  --, --CH 2  CH 2  -- or a single bond, and 
     n is 0 or 1, 
     as components of chiral tilted smectic phases.

The invention relates to the use of trifluorotoluene derivatives of theformula I ##STR2## in which R¹ is alkyl having 1 to 12 carbon atoms inwhich, in addition, one or more non-neighboring CH₂ groups may bereplaced by --O--, --CO--, --O--CO--, --CO--O--, --O--CO--O--,--CH--halogen, --CH--CN-- and/or --CH═CH--,

A¹ and A², in each case independently of one another, are 1,4-phenylenein which, in addition, one or more CH groups may be replaced by N,trans-1,4-cyclohexylene in which, in addition, one or morenon-neighboring CH₂ groups may be replaced by --O-- and/or --S--, or1,4-bicyclo(2.2.2)octylene, each of which is unsubstituted ormonosubstituted or polysubstituted by halogen, nitrile and/or CH₃,

Z¹ and Z², in each case independently of one another, are --CO--O--,--O--CO--, --CH₂ O--, --OCH₂ --, --CH₂ CH₂ -- or a single bond, and

n is 0 or 1,

as components of chiral tilted smectic phases, and also to smecticliquid-crystalline phases, in particular chiral tilted smectic phases,containing compounds of the formula I. The invention furthermore relatesto novel pyrimidine and pyridine compounds, novel cyclohexanederivatives and novel dioxane derivatives of the formula I.

Chiral tilted smectic liquid-crystallie phases having ferroelectricproperties can be produced by adding a suitable chrial dope to basemixture having one or more tilted smectic phases (L. A. Beresnev et al.,Mol. Cryst. Liq. Cryst. 89, 327 (1982); H. R. Brand et al., J. Physique44, (lett.), L-771 (1983). Such phases can be used as dielectrics forrapidly switching displays which are based on the principle described byClark and Lagerwall, of SSFLC technology (N. A. Clark and S. T.Lagerwall, Appl. Phys. Lett. 36, 899 (1980); U.S. Pat. No. 4,367,924) onthe basis of the ferroelectric properties of the chiral tilted phase. Inthis phase, the extended molecules are arranged in layers, the moleculeshaving a tilt angle to the layer perpendiculars. On proceeding fromlayer to layer, the tilt angle changes through a small angle withrespect to an axis which is perpendicular to the layers, so that ahelical structure is formed. In displays which are based on theprinciple of SSFLC technology, the smectic layers are arrangedperpendicular to the plates of the cells. The helical arrangement of thetilt directions of the molecules is suppressed by a very smallseparation of the plates (about 1-2 μm). The longitudinal axes of themolecule are thereby forced to arrange themselves in a plane parallel tothe plates of the cell, whereby two distinct tilt orientations areproduced. By applying a suitable alternating electrical field, it ispossible to switch to and fro between these two states in theliquid-crystalline phase having spontaneous polarization. This switchingprocess is significantly faster than in conventional twisted cells(TN-LCDs), which are based on nematic liquid crystals.

A major disadvantage for many applications of the materials currentlyavailable having chiral tilted smectic phases (such as, for example,Sc*) is that the S_(A) phase, above the Sc* phase, which is necessaryfor good orientation capability in the display, often does not arise ornot in the desired temperature range.

It has now been found that the use of compounds of the formula I ascomponents of chiral tilted smectic mixtures can substantially lessenthe disadvantages mentioned. The compounds of the formula I are thushighly suitable as components of chiral tilted smecticliquid-crystalline phases. In particular, chiral tilted smecticliquid-crystalline phases which have favorable ferroelectric phaseregions, in particular broad Sc* phase regions, and are particularlystable chemically, and S_(A) phases, above the Sc phase, which arefavorable for the orientation in the display, have a favorable pitchheight and have values for spontaneous polarization which are high forsuch phases, can be produced with their aid. P is the spontaneouspolarization in nC/cm².

The invention thus relates to the use of the compounds of the formula Ias components of (chiral tilted) smectic liquid-crystalline phases. Theinvention furthermore relates to smectic liquid-crystalline phases, inparticular chiral tilted smectic phases, which contain at least onecompound of the formula I, and to liquid-crystal display elements, inparticular electrooptical display elements, which contain such phases.The invention furthermore relates to novel pyrimidine and pyridinecompounds of the formula I in which one of the A¹ and A² groups ispyrimidine- or pyridine-2,5-diyl, and to the cyclohexane derivatives ofthe forula II and the dioxane derivatives of the formula III.

The compounds of the formula I can have straight-chain or branched winggroups R¹. Compounds having branched wing groups can be employed in theform of the racemate or as optically active compounds. Achiral basemixtures of compounds of the formula I and, if appropriate, furtherachiral components can be doped with chiral compounds of the formula 1or alternatively with other chiral compounds, in order to obtain chiraltilted smectic phases.

The compounds of the formula I include, in particular, compounds of thesubformulae Ia to Id: ##STR3##

Of these, those of the subformula Ib are particularly preferred (Phe is1,4-phenylene).

In the compounds of the formulae above and below, R¹ is preferably R--,R--O--, R--O--CO--, R--O--COO-- or R--CO--O--. R is preferably astraight-chain alkyl group preferably having 5 to 12 carbon atoms, inwhich, in addition, one or two nonterminal CH₂ groups can be replaced by--O--, --O--CO--, --CHCH₃ --, --CHCN--, --CH--halogen, --CHCH₃ --O--and/or --CH═CH--. R is preferably, for example, pentyl, hexyl, heptyl,octyl, nonyl, decyl, undecyl or dodecyl, furthermore methyl, ethyl,propyl, butyl, 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-,4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-,6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6- 7-, 8- or 9-oxadecyl,1,3-dioxabutyl (=methoxymethoxy), 1,3-, 1,4- or 2,4-dioxapentyl, 1,3-,1,4-, 1,5-, 2,4-, 2,5- or 3,5-dioxahexyl, 1,3-, 1,4-, 1,5-, 1,6- 2,4-,2,5-, 2,6-, 3,5-, 3,6- or 4,6-dioxaheptyl, 1,4-dioxaoctyl,1,4,7-trioxaoctyl, 1,4-dioxanonyl or 1,4-dioxadecyl.

Compounds of the formula I and of the subformulae above and below,having a branched wing group R¹ can occasionally be important due tobetter solubility in conventional liquid-crystalline base materials, butin particular, when they are optically active, as chiral dopes forchiral tilted smectic phases. However, such compounds are also suitableas components of nematic liquid-crystalline phases, in particular forprevention of reverse twist. Branched groups of this type generallycontain one or two chain branches. In a preferred fashion, theasymmetrical carbon atom is linked to two differently substituted carbonatoms, one H atom and one substituent, selected from the groupcomprising halogen (in particular F, Cl or Br), alkyl or alkoxy in eachcase having 1 to 5 carbon atoms, and CN. The optically active organicradical R¹ or R² preferably has the formula ##STR4## in which X is--CO--O--, --O--CO--, --O--CO--O--, --CO--, --O--, --S--, --CH═CH--,--CH═CH--COO-- or a single bond,

Q is alkylene having 1 to 5 carbon atoms, in which, in addition, one CH₂group which is not linked to X may be replaced by --O--, --CO--,--O--CO--, --CO--O-- or --CH═CH--, or a single bond,

Y is CN, halogen, methyl or methoxy, and

R is an alkyl group having 1 to 18 carbon atoms which is different to Yand in which, in addition, one or two non-neighboring CH₂ groups may bereplaced by --O--, --CO--, --O--CO--, --CO--O-- and/or --CH═CH--.

X is preferably --O--, --CO--O--, --O--CO--, --CH═CH--COO-- (trans) or asingle bond. --O--, --CO--O-- and --O--CO-- are particularly preferred.

Q is preferably --CH₂ --, --CH₂ CH₂ -- or a single bond, particularlypreferably a single bond.

Y is preferably CH₃, --CN or Cl, particularly preferably --CN.

R is preferably straight-chain alkyl having 1 to 10, in particularhaving 1 to 7 carbon atoms in which, if appropriate, a CH₂ group may bereplaced by --O--, --O--CO-- or --CO--O--.

Preferred branched radicals are isopropyl, 2-butyl (=1-methylpropyl),isobutyl (=2-methylpropyl, isobutyl (=2-methylpropyl), 2-methylbutyl,isopentyl (=3-methylbutyl), 2-methylpentyl, 3-methylpentyl,2-ethylhexyl, 2-propylpentyl, 2-octyl, 3,7-dimethyloctyl, isopropoxy,2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy,3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, 1-methylheptoxy,2-oxa-3-methylbutyl, 3-oxa-4-methylpentyl, 2-octyloxy,3,7-dimethyloctyloxy, 2-chloropropionyloxy, 2-chloro-3-methylbutyryloxy,2-chloro-4-methylvaleryloxy, 2-chloro-3-methylvaleryloxy,2-methyl-3-oxapentyl and 2-methyl-3-oxahexyl.

In the case where n=1, one of the Z¹ and Z₂ groups is preferably asingle bond. A¹ and A² are preferably 1,4 -phenylene,trans-1,4-cyclohexylene or pyrimidine-2,5-diyl. The compounds of theformula I preferably contain no more than one 1,4-phenylene group inwhich one or more CH groups are replaced by N.

Of the compounds of the formula I and of the subformulae above andbelow, those are preferred in which at least one of the radicalscontained therein has one of the preferred meanings given.

The compounds of the formula I are prepared by methods which are knownper se, as described in the literature (for example in the standardworks such as HoubenWeyl, Methoden der Organischen Chemie [Methods ofOrganic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise underreaction conditions which are known and suitable for the reactionsmentioned. In this case, use can also be made of variants which areknown per se but are not described in greater detail here.

If desired, the starting materials can also be formed in situ by notisolating them from the reaction mixture, but instead immediatelyreacting them further to form the compounds of the formula I.

Some of the compounds of the formula I are known (for example GermanOffenlegungsschrift 2,937,911 and DD 144,409) and some are novel.Particularly preferred are the novel compounds of the formula I in whichone of the A¹ and A² groups is pyrimidine-2,5-diyl or pyridine-2,5-diyl,and, in the case where n=1 and A¹ =pyrimidine-2,5-diyl, Z² is CH₂ O--,--OCH₂ --, --CH₂ CH₂ -- or a single bond. Particularly preferred are thenovel compounds of the subformulae Ib and Ic: ##STR5## in which A¹ ispyrimidine-2,5-diyl or pyridine-2,5-diyl

A² is 1,4-phenylene,

Phe is 1,4-phenylene,

Z¹ and Z² are in each case --CH₂ O--, --OCH₂ --, --CH₂ CH₂ -- or asingle bond, and

R¹ has the meaning given in the case of formula I.

In these preferred pyridine and pyrimidine compounds, one of the Z¹ andZ² groups is preferably --CH₂ O--, --OCH₂ -- or --CH₂ CH₂ --, and theother group is a single bond. Likewise preferred are pyridine andpyrimidine compounds in which Z¹ and Z² are single bonds. R¹ ispreferably straight-chain alkyl having 2 to 12 carbon atoms, inparticular having 3 to 10 carbon atoms.

Furthermore preferred are the novel cyclohexane derivatives of theformula II ##STR6## in which R¹ is alkyl having 1 to 12 carbon atoms inwhich, in addition, one or more non-neighboring CH₂ groups may bereplaced by --O--, --CO--, --O--CO--, --CO--O--, --O--CO--O--,--CH--halogen, --CH--CN-- and/or --CH═CH--,

Z¹ and Z², in each case independently of one another, are --CO--O--,--O--CO--, --CH₂ O--, --OCH₂ -- or --CH₂ CH₂, and one of the Z¹ and Z²groups is alternatively a single bond,

n is 0 or 1

with the proviso that, in the case where n=1 and Z¹ = a single bond, Z²is --CO--O--, --CH₂ O--, --OCH₂ -- or --CH₂ CH₂.

R¹ here is preferably straight-cain alkyl having 2 to 7 carbon atoms. Inthe case where n=O, Z¹ is preferably --COO--, --CH₂ CH₂ -- or a singlebond. In the case where n=1, one of the Z¹ and Z² groups is preferably asingle bond and the other Z¹ or Z² group is --CH₂ CH₂ -- or --COO--,preferably --CH₂ CH₂ --. Particularly preferred compounds are those ofthe subformulae IIa to IIg: ##STR7##

Furthermore preferred are the novel dioxane derivatives of the formulaIII ##STR8## in which R¹ is alkyl having 1 to 12 carbon atoms in which,in addition, one or more non-neighboring CH₂ groups may be replaced by--O--, --CO--, --O--CO--, --CO--O--, --O--CO--O--, --CH--halogn,--CH--CN-- and/or --CH═CH--.

R¹ here is preferably straight-chain alkyl having 2 to 7 carbon atoms.

The compounds of the formulae II and III are suitable not only as dopesfor ferroelectric liquid-crystalline phases, but also, in particular,are excellent components of nematic liquid-crystalline phases.

The nematic liquid-crystalline phases according to the invention arelikewise subject-matter of the invention and comprise 2 to 15,preferably 3 to 12, components, including at least one compound of theformula II and/or III. The other components are preferably selected fromnematic or nematogenic substances, in particular known substances fromthe classes comprising the azoxybenzenes, benzylideneanilines,biphenyls, terphenyls, phenyl- or cyclohexylbenzoates, phenyl orcyclohexyl cyclohexanecarboxylates, phenylcyclohexanes,phenylbicyclohexanes, cyclohexylbiphenyls, cyclohexylcyclohexanes,cyclohexylnaphthalenes, 1,4-bis-cyclohexylbenzenes,4,4'-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl-or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes,1-phenyl-2-cyclohexylethanes, optionally halogenated stilbenes, benzylphenyl ether, tolanes and substituted cinnamic acids.

The most important compounds which are suitable as components of suchliquid-crystalline phases can be characterized by the formula II'

    R'-L-G-E-R"                                                II'

in which L and E are each a carbocyclic or heterocyclic ring system fromthe group formed from 1,4-disubstituted benzene and cyclohexane rings,4,4'-disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexanesystems, 2,5-disubstituted pyrimidine and 1,3-dioxane rings,2,6disubstituted naphthalene, di- and tetrahydronaphthalene, quinazolineand tetrahydroquinazoline, G is

    ______________________________________                                        --CH═CH--    --N(O)═N--                                               --CH═CY--    --CH═N(O)--                                              --C.tbd.C--      --CH.sub.2 --CH.sub.2 --                                     --CO--O--        --CH.sub.2 --O--                                             --CO--S--        --CH.sub.2 --S--                                             --CH═N--     --COO--Phe--COO--                                            ______________________________________                                    

or a C--C single bond, Y is halogen, preferably chlorine, or CN, and R'and R" are alkyl, alkenyl, alkoxy, oxaalkyl, alkanoyloxy oralkoxycarbonyloxy having up to 18, preferably up to 8, carbon atoms, orone of these radicals is alternatively CN, NC, NCS, NO₂, CH₃, F, Cl orBr.

In most of these compounds, R' and R" are different to one another, oneof these radicals usually being an alkyl or alkoxy group. However, othervariants of the proposed substituents are also customary. Many suchsubstances, or alternatively mixtures thereof, are commerciallyavailable. All these substances can be prepared by methods which areknown from the literature.

The phases according to the invention contain about 0.1 to 99,preferably 10 to 95, % of one or more compounds of the formula II and/orIII.

These nematic phases are distinguished by favorable phase regions, lowviscosity, low optical anisotropy and favorable threshold voltages.

The chiral tilted smectic phases according to the invention preferablycontain at least two, in particular at least three, compounds.Particular preference is given to chiral tilted smecticliquid-crystalline phases, according to the invention, whose achiralbase mixture contains at least one other component having negative ornumerically small positive dielectric anisotropy in addition to at leastone compound of the formula I. This/these further component(s) of thechiral base mixture can comprise 1 to 50%, preferably 10 to 25%, of thebase mixture. Suitable further components having numerically smallpositive or negative dielectric anisotropy are compounds of thesubformulae Va to Vp: ##STR9##

R⁴ and R⁵ are in each case preferably straight-chain alkyl, alkoxy,alkanoyloxy or alkoxycarbonyl in each case having 3 to 12 carbon atoms.X is preferably 0. n is 0 or 1.

Particularly preferred compounds are those of the subformulae Va, Vb,and Vf in which R⁴ and R⁵ are in each case straight-chain alkyl oralkoxy in each case having 5 to 10 carbon atoms.

The compounds of the subformulae Vc, Vh and Vi are suitable as additivesfor lowering the melting point and are normally added to the basemixtures in amounts of not more than 5%, preferably 1 to 3%. R⁴ and R⁵in the compounds of the subformulae Vc, Vh and Vi are preferablystraight-chain alkyl having 2 to 7, preferably 3 to 5, carbon atoms. Afurther class of compounds which is suitable for lowering the meltingpoint in the phases according to the invention is that of the formula##STR10## in which R⁴ and R⁵ have the preferred meaning given for Vc, Vhand Vi.

Suitable further components having negative dielectric anisotropy arefurthermore compounds containing the structural element B or C.##STR11##

Preferred compounds of this type correspond to the formulae VIb and VIc:##STR12##

R' and R" are in each case preferably straight-chain alkyl or alkoxygroups in each case having 2 to 10 carbon atoms. Q¹ and Q² are in eachcase 1,4-phenylene, trans-1,4-cyclohexylene, 4,4'-biphenylyl,4-(trans-4-cyclohexyl)-phenyl or trans,trans-4,4'-bicyclohexyl, or oneof the Q¹ and Q² groups is alternatively a single bond.

Q³ and Q⁴ are in each case 1,4-phenylene, 4,4'-biphenylyl ortrans-1,4-cyclohexylene. One of the Q³ and Q⁴ groups can alternativelybe 1,4-phenylene, in which at least one CH group is replaced by N. R'"is an optically active radical having an asymmetrical carbon ##STR13##atom and having the structure --CH--, --CH-- or --CH--. Particularlypreferred compounds of the formula VIc are those of the formula VIc':##STR14## in which A is 1,4-phenylene or trans-1,4-cyclohexylene, and nis 0 or 1.

The phases according to the invention are produced in a fashion which isconventional per se. In general, the components are dissolved in oneanother, expediently at elevated temperature.

Through suitable additives, the liquid-crystalline phases can bemodified according to the invention so that they can be used in alltypes of liquid-crystal display elements which have hitherto becomeknown.

The following examples are intended to illustrate the invention withoutrepresenting a limitation. Above and below, percentage data arepercentages by weight; all temperatures are given in degrees Celsius.Furthermore: C denotes the crystalline solid state, S denotes thesmectic phase (the index characterizes the phase type), N denotes thenematic state, Ch denotes the cholesteric phase and I denotes theisotropic phase. The number between two symbols gives the conversiontemperature in degrees Celsius. "Conventional work-up" means that wateris added, the mixture is extracted with methylene chloride, the organicphase is separated off, dried and evaporated, and the product ispurified by crystallization and/or chromatography.

EXAMPLE 1

A liquid-crystalline phase comprising

7% of p-(5-heptylpyrimidin-2-yl)-phenyl p-pentylbenzyl ether,

9% of p-(5-heptylpyrimidin-2-yl)-phenyl p-hexylbenzyl ether,

3% of p-(5-nonylpyrimidin-2-yl)-phenyl p-pentylbenzyl ether,

5% of p-(5-nonylpyrimidin-2-yl)-phenyl p-heptylbenzyl ether,

25% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-butylcyclohexane,

3% of optically active 2-octylp-[5-nonylpyrimidin-2-yl)phenoxymethyl]-benzoate

12% of optically active r-4-(5-hexylpyrimidin-2-yl)phenyl2-chloropropionate and

6% of p-[5-nonylpyrimidin-2-yl)-phenoxymethyl]-trifluorotoluene

exhibits C 15° Sc* 83° S_(A) * 87° CH 98° I, a spontaneous polarizationof 12.4 nC/cm² and a tilt angle of 26°, in each case at 20° C.

EXAMPLE 2

A liquid-crystalline phase comprising

7% of p-(5-heptylpyrimidin-2-yl)-phenyl p-pentylbenzyl ether,

9% of p-(5-heptylpyrimidin-2-yl)-phenyl p-hexylbenzyl ether,

3% of p-(5-nonylpyrimidin-2-yl)-phenyl p-pentylbenzyl ether,

5% of p-(5-nonylpyrimidin-2-yl)-phenyl p-heptylbenzyl ether,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

5% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

15% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-butylcyclohexane,

15% of r-1-cyano-cis-4-(4'-octylbiphenyl-4-yl)-1-pentylcyclohexane,

3% of optically active 2-octylp-[5-nonylpyrimidin-2-yl)phenoxymethyl]-benzoate

12% of optically active r-4-(5-hexylpyrimidin-2-yl)-phenyl2-chloropropionate and

6% of p-[5-nonylpyrimidin-2-yl)-phenoxymethyl]-trifluorotoluene

exhibits C 0° Sc* 72° S_(A) * 83° Ch 92° I and a spontaneouspolarization of 10.5 nC/cm² at 20° C.

EXAMPLE 3

A liquid-crystalline phase comprising

7% of p-(5-heptylpyrimidin-2-yl)-phenyl p-pentylbenzyl ether,

9% of p-(5-heptylpyrimidin-2-yl)-phenyl p-hexylbenzyl ether,

3% of p-(5-nonylpyrimidin-2-yl)-phenyl p-pentylbenzyl ether,

5% of p-(5-nonylpyrimidin-2-yl)-phenyl p-heptylbenzyl ether,

20% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

5% of 2-p-octyloxyphenyl-5-heptylpyrimidine,

15% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-butylcyclohexane,

15% of r-1-cyano-cis-4-(4'-heptylbiphenyl-4-yl)-1-hexylcyclohexane,

15% of optically active R-4-(5-hexylpyrimidin-2-yl)phenyl2-chloropropionate and

6% of p-[5-nonylpyrimidin-2-yl)-phenoxymethyl]-trifluorotoluene

exhibits C 0° Sc* 73° S_(A) * 78° Ch 92° I, a spontaneous polarizationof 12.3 nC/cm² and a tilt angle of 30°, in each case at 20° C.

EXAMPLE 4

0.03 m of 4-(4-propylphenyl)-benzoyl chloride is added dropwise withstirring to a solution of 0.03 m of p-(trifluoromethyl)-phenol in 50 mlof pyridine at 0°-5°, the mixture is stirred for a further 20 hours atroom temperature, and worked up as conventional. p-Trifluoromethyl4-(4-propylphenyl)-benzoate is obtained.

The following are prepared analogously:

p-trifluoromethyl p-(trans-4-propylcyclohexyl)-benzoate

p-trifluoromethyl p-(trans-4-butylcyclohexyl)-benzoate

p-trifluoromethyl p-(trans-4-pentylcyclohexyl)-benzoate

p-trifluoromethyl p-(trans-4-hexylcyclohexyl)-benzoate

p-trifluoromethyl p-(trans-4-heptylcyclohexyl)-benzoate

p-trifluoromethyl p-(trans-4-nonylcyclohexyl)-benzoate

p-trifluoromethyl p-propylbenzoate

p-trifluoromethyl p-butylbenzoate

p-trifluoromethyl p-pentylbenzoate

p-trifluoromethyl p-hexylbenzoate

p-trifluoromethyl p-heptylbenzoate

p-trifluoromethyl p-nonylbenzoate

EXAMPLE 5

0.01 m of p-(trifluoromethyl)-benzoyl chloride is added dropwise withstirring to a solution of 0.01 m of 2-p-hydroxyphenyl-5-nonylpyrimidinein 20 ml of pyridine at 0°-5°, the mixture is stirred for 20 hours atroom temperature, and worked up as usual.p-(5-Nonylpyrimidin-2-yl)-phenmyl p-(trifluoromethyl)-benzoate isobtained.

The following are prepared analogously:

p-(5-octylpyrimidin-2-yl)-phenyl p-(trifluoromethyl)-benzoate

p-(5-heptylpyrimidin-2-yl)-phenyl p-(trifluoromethyl)-benzoate

p-(5-hexylpyrimidin-2-yl)-phenyl p-(trifluoromethyl)-benzoate

p-(5-pentylpyrimidin-2-yl)-phenyl p-(trifluoromethyl)-benzoate

EXAMPLE 6

A mixture of 0.03 m of p-(trans-4-pentylcyclohexyl)-benzyl bromide(obtainable from p-(trans-4-pentylcyclohexyl)-benzoic acid), 0.03 m ofp-(trifluoromethyl)phenol, 0.03 m of potassium carbonate and 40 ml ofDMF are warmed to 120° while stirring under the exclusion of air and,after cooling, worked up as usual.

p-(Trifluoromethyl)-phenyl p-(trans-4-pentylcyclohexyl)-benzyl ether isobtained.

The following are prepared analogously:

p-(trifluoromethyl)-phenyl p-(trans-4-hexylcyclohexyl)-benzyl ether

p-(trifluoromethyl)-phenyl p-(trans-4-heptylcyclohexyl)-benzyl ether

p-(trifluoromethyl)-phenyl p-(trans-4-octylcyclohexyl)-benzyl ether

p-(trifluoromethyl)-phenyl p-(trans-4-nonylcyclohexyl)-benzyl ether

EXAMPLE 7

Analogously to Example 6, p-(5-nonylpyrimidin-2-yl)-phenylp-(trifluoromethyl)-benzyl ether is obtained fromp-(trifluoromethyl)-benzyl bromide (obtainable fromp-(trifluoromethyl)-benzyl alcohol and HBr),2-p-hydroxyphenyl-5-nonylpyrimidine, K₂ CO₃ and DMF.

The following are prepared analogously:

p-(5-octylpyrimidin-2-yl)-phenyl p-(trifluoromethyl)-benzyl ether

p-(5-heptylpyrimidin-2-yl)-phenyl p-(trifluoromethyl)-benzyl ether

p-(5-hexylpyrimidin-2-yl)-phenyl p-(trifluoromethyl)-benzyl ether

(S)-p-[5-(6-methyloctyl)-pyrimidin-2-yl]-phenylp-(trifluoromethyl)-benzyl ether

p-(5-octylpyridin-2-yl)-phenyl p-(trifluoromethyl)-benzyl ether

p-(5-heptylpyridin-2-yl)-phenyl p-(trifluoromethyl)-benzyl ether

p-(5-hexylpyridin-2-yl)-phenyl p-(trifluoromethyl)-benzyl ether

p-(5-pentylpyridin-2-yl)-phenyl p-(trifluoromethyl)-benzyl ether

p-(5-butylpyridin-2-yl)-phenyl p-(trifluoromethyl)-benzyl ether

p-(5-propylpyridin-2-yl)-phenyl p-(trifluoromethyl)-benzyl ether

EXAMPLE 8

In an autoclave, 0.1 m of p-[2-(p-pentylphenyl)ethyl]-benzoic acid(obtainable through hydrolysis of the corresponding benzonitrile) and0.4 m of SF₄ are shaken for 7 hours at 130°. The reaction mixture ischromatographed over silica gel.p-[2-(p-Pentylphenyl)-ethyl]trifluoromethylbenzene is obtained.

The following are prepared analogously:

p-[2-(2-p-hexylphenyl)-ethyl]-trifluoromethylbenzene

p-[2-(p-heptylphenyl)-ethyl]-trifluoromethylbenzene

p-[2-(p-octylphenyl)-ethyl]-trifluoromethylbenzene

p-[2-(p-nonylphenyl)-ethyl]-trifluoromethylbenzene

p-(5-propylpyrimidin-2-yl)-trifluoromethylbenzene, m.p. 87°

p-(5-pentylpyrimidin-2-yl)-trifluoromethylbenzene, m.p. 50°

p-[p-(5-propylpyrimidin-2-yl)-phenyl]-trifluoromethylbenzene, m.p. 172°

p-(5-propylpyridin-2-yl)-trifluoromethylbenzene

p-(5-pentylpyridin-2-yl)-trifluoromethylbenzene

p-(5-heptylpyridin-2-yl)-trifluoromethylbenzene

EXAMPLE 9

A solution of 1.9 g of1-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]-2-(p-trifluorotolyl)-ethene(obtainable through Heck coupling oftrans-4-(trans-4-propylcyclohexyl)-1-vinylcyclohexane withp-bromotrifluorotoluene) in 50 ml of tetrahydrofuran is hydrogenated atroom temperature on 1 g of Pd/C (5%). After conventional work-up,1-[trans-4-(trans-4-propylcyclohexyl)-cyclohexyl]-2-(p-trifluorotolyl)-ethane,m.p. 50°, c.p. 117°.

The following are prepared analogously:

1-[trans-4-(trans-4-ethylcyclohexyl)-cyclohexyl]-2-(p-trifluorotolyl)ethane

1-[trans-4-butylcyclohexyl)-cyclohexyl]-2-(p-trifluorotolyl)ethane

1-[trans-4-(trans-4-pentylcyclohexyl)-cyclohexyl]-2-(p-trifluorotolyl)ethan

1-[trans-4-(trans-4-hexylcyclohexyl)-cyclohexyl]-2-(p-trifluorotolyl)ethane

1-[trans-4-heptylcyclohexyl)-cyclohexyl]-2-(p-trifluorotolyl)ethane

1-(trans-4-ethylcyclohexyl)-2-(p-trifluorotolyl)-ethane

1-(trans-4-propylcyclohexyl)-2-(p-trifluorotolyl)-ethane

1-(trans-4-butylcyclohexyl)-2-(p-trifluorotolyl)-ethane

1-(trans-4-pentylcyclohexyl)-2-(p-trifluorotolyl)-ethane

1-(trans-4-hexylcyclohexyl)-2-(p-trifluorotolyl)-ethane

1-(trans-4-heptylcyclohexyl)-2-(p-trifluorotolyl)-ethane

EXAMPLE 10

A solution of 65 g of 4-n-pentylcyclohexanone in 200 ml of diethyl etheris added dropwise over the course of one hour with stirring and coolingto a Grignard solution prepared from 115 g of p-bromotrifluorotolueneand 13 g of magnesium turnings in 400 ml of diethyl ether. The reactionmixture is heated to boiling for a further hour and then poured into asolution of 50 ml of concentrated hydrochloric acid in 1 liter of icewater. The ether phase is separated off, and the aqueous phase isextracted by shaking twice with 100 ml of diethyl ether in each case.The combined ether phases are washed with 5% aqueous sodium hydrogencarbonate solution until neutral, dried over sodium sulfate andevaporated. The residue is subjected to separation over a column packedwith silica gel. The 4-n-pentyl-cyclohexanol eluted using petroleumether (boiling range 40°-60°) is dissolved in 1 liter of ethanol andhydrogenated for 72 hours at room temperature and atmospheric pressurein the presence of 75 g of moist Raney nickel. After the catalyst hasbeen filtered off and the ethanol has been removed by distillation, theresidue is worked up as usual and purified by chromatography.p(Trans-4-n-pentylcyclohexyl)-trifluorotoluene, m.p. 10°, c.p. -60°, isobtained.

The following are obtained analogously:

p-(-trans-4-ethylcyclohexyl)-trifluorotoluene

p-(-trans-4-propylcyclohexyl)-trifluorotoluene

p-(-trans-4-butylcyclohexyl)-trifluorotoluene

p-(-trans-4-hexylcyclohexyl)-trifluorotoluene

p-(-trans-4-heptylcyclohexyl)-trifluorotoluene

p-(trans-4-[2-(trans-4-ethylcyclohexyl)-ethyl]-cyclohexyl)-trifluorotoluene

p-(trans-4-[2-(trans-4-propylcyclohexyl)-ethyl]-cyclohexyl)-trifluorotoluene

p-(trans-4-[2-(trans-4-butylcyclohexyl)-ethyl]-cyclohexyl)-trifluorotoluene

p-(trans-4-[2-(trans-4-pentylcyclohexyl)-ethyl]-cyclohexyl)-trifluorotoluene

p-(trans-4-[2-(trans-4-hexylcyclohexyl)-ethyl]-cyclohexyl)-trifluorotoluene

p-(trans-4-[2-(trans-4-heptylcyclohexyl)-ethyl]-cyclohexyl)-trifluorotoluene

EXAMPLE 11

A solution of 29.3 g oftrans-4-(trans-4-n-pentylcyclohexyl)-cyclohexanecarbonyl chloride in 120ml of toluene is added dropwise in the course of 2 hours with stirringto a boiling solution of 16.2 g of p-trifluoromethylphenol and 10 ml ofpyridine in 120 ml of toluene. The reaction mixture is refluxed for afurther 3 hours and then evaporated. The residue is worked up asconventional. p-Trifluoromethylphenyltrans-4-(trans-4-n-pentylcyclohexyl)-cyclohexanecarboxylate is obtained.

The following are prepared analogously:

p-trifluoromethylphenyltrans-4-(trans-4-ethylcyclohexyl)-cyclohexanecarboxylate

p-trifluoromethylphenyltrans-4-(trans-4-propylcyclohexyl-cyclohexanecarboxylate

p-trifluoromethylphenyltrans-4-(trans-4-butylcyclohexyl)-cyclohexanecarboxylate

p-trifluoromethylphenyltrans-4-(trans-4-hexylcyclohexyl)-cyclohexanecarboxylate

p-trifluoromethylphenyltrans-4-(trans-4-heptylcyclohexyl)-cyclohexanecarboxylate

p-trifluoromethylphenyl trans-4-ethylcyclohexanecarboxylate

p-trifluoromethylphenyl trans-4-propylcyclohexanecarboxylate

p-trifluoromethylphenyl trans-4-butylcyclohexanecarboxylate

p-trifluoromethylphenyl trans-4-pentylcyclohexanecarboxylate

p-trifluoromethylphenyl trans-4-hexylcyclohexanecarboxylate

p-trifluoromethylphenyl trans-4-heptylcyclohexanecarboxylate

EXAMPLE 12

A nematic liquid-crystalline phase comprising

30% of trans-4-pentylcyclohexyl-trifluorotoluene

12% of trans-1-p-methoxyphenyl-4-propylcyclohexane

12% of trans-1-p-ethoxyphenyl-4-propylcyclohexane

10% of trans-1-p-butoxyphenyl-4-propylcyclohexane

10% of 4-ethyl-4'-(trans-4-propylcyclohexyl)-biphenyl

10% of 4-ethyl-4'-(trans-4-pentylcyclohexyl)-biphenyl

5% of 4,4'-bis-(trans-4-propylcyclohexyl)-biphenyl,

5% of 4,4'-bis-(trans-4-pentylcyclohexyl)-biphenyl and

6% of4-(trans-4-pentylcyclohexyl)-4'-(trans-4-propylcyclohexyl)-biphenyl

exhibits a clear point of 70°, an optical anisotropy of 0.098 and aviscosity of 14 mPa.s at 20°.

EXAMPLE 13

A nematic liquid-crystalline phase is produced comprising

30% of1[trans-4-propylcyclohexyl)-cyclohexyl]-2-(p-trifluorotolyl)-ethane

12% of trans-1-p-methoxyphenyl-4-propylcyclohexane

12% of trans-1-p-ethoxyphenol-4-propylcyclohexane

10% of trans-1-p-butoxyphenyl-4-propylcyclohexane

10% of 4-ethyl-4'-(trans-4-propylcyclohexyl)-biphenyl

10% of 4-ethyl-4'-(trans-4-pentylcyclohexyl)-biphenyl,

5% of 4,4'-bis-(trans-4-propylcyclohexyl)-biphenyl,

5% of 4,4'-bis-(trans-4-pentylcyclohexyl)-biphenyl and

6% of4-(trans-4-pentylcyclohexyl)-4'-(trans-4-propylcyclohexyl)-biphenyl.

EXAMPLE 14

A nematic liquid-crystalline phase comprising

15% of trans-1-p-methoxyphenyl-4-propylcyclohexane

15% of trans-1-(trans-4-propylcyclohexyl)-4-methoxycyclohexane

10% of trans-1-(trans-4-propylcyclohexyl)-4-propoxycyclohexane

10% of trans-1-(trans-4-pentylcyclohexyl)-4-methoxycyclohexane

10% of trans-1-(trans-4-pentylcyclohexyl)-4-ethoxycyclohexane

10% of p-trifluoromethylphenyltrans-4-(trans-4-propylcyclohexyl)-cyclohexanecarboxylate

10% of p-trifluoromethylphenyltrans-4-(trans-4-butylcyclohexyl)-cyclohexanecarboxylate

10% of p-trifluoromethylphenyltrans-4-(trans-4-pentylcyclohexyl)-cyclohexanecarboxylate and

10% of p-trifluoromethylphenyltrans-4-(trans-4-heptylcyclohexyl)-cyclohexanecarboxylate

exhibits a clear point of 72°, an optical anisotropy of 0.086 and aviscosity of 18 mPa.s at 20°.

EXAMPLE 15

A nematic liquid-crystalline phase comprising

20% of p-trifluoromethylphenyl trans-4-phenylcyclohexanecarboxylate

10% of p-methoxyphenyl trans-4-propylcyclohexanecarboxylate

10% of p-ethoxyphenyl trans-4-propylcyclohexanecarboxylate

10% of p-methoxyphenyl trans-4-butylcyclohexanecarboxylate

10% of p-ethoxyphenyl trans-4-butylcyclohexanecarboxylate

10% of p-propylphenyltrans-4-(trans-4-propylcyclohexyl)-cyclohexanecarboxylate

10% of p-pentylphenyl trans4-(trans-4-propylcyclohexyl)cyclohexanecarboxylate

10% of p-pentylphenyltrans-4-(trans-4-butylcyclohexyl)-cyclohexancarboxylate and

10% of p-propylphenyltrans-4-(trans-4-butylcyclohexyl-cyclohexanecarboxylate

exhibits a clear point of 85°, an optical anisotropy of 0.094 and aviscosity of 14 mPa.s at 20°.

EXAMPLE 16

A ferroelectric liquid-crystalline phase comprising

7% of p-(5-heptylpyrimidin-2-yl)-phenyl p-pentylbenzyl ether

9% of p-(5-heptylpyrimidin-2-yl)-phenyl p-hexylbenzyl ether

3% of p-(5-nonylpyrimidin-2-yl)-phenyl p-pentylbenzyl ether

5% of p-(5-nonylpyrimidin-2-yl)-phenyl p-heptylbenzyl ether

28% of 2-p-nonyloxyphenyl-5-nonylpyrimidine,

30% of r-1-cyano-cis-4-(4'-octyloxybiphenyl-4-yl)-1-butylcyclohexane,

3% of optically active 2-octylp-[5-nonylpyrimidin-2-yl)phenoxymethyl]-benzoate

12% of optically active R-4-(5-hexylpyrimidin-2-yl)phenyl2-chloropropionate and

3% of p-(trans-4-n-pentylcyclohexyl)-trifluorotoluene exhibit a broadS_(A) phase.

EXAMPLE 17

An equimolar mixture of p-trifluoromethylbenzaldehyde and2-pentylpropane-1,3-diol in toluene is boiled on a water separator withcatalysis by p-toluenesulfonic acid. When the water separation iscomplete and after conventional work-up,p-(trans-5-n-pentyl-1,3-dioxan-2-yl)trifluorotoluene, m.p. 44.3°,Δε=+12.9, is obtained.

The following are prepared analogously:

p-(trans-5-ethyl-1,3-dioxan-2-yl)-trifluorotoluene

p-(trans-5-propyl-1,3-dioxan-2-yl)-trifluorotoluene, m.p. 57.0°,Δε=+15.8

p-(trans-5-butyl-1,3-dioxan-2-yl)-trifluorotoluene

p-(trans-5-heptyl-1,3-dioxan-2-yl)-trifluorotoluene

EXAMPLE 18

A nematic liquid-crystalline phase is produced comprising

30% of p-(trans-5-n-pentyl-1,3-dioxan-2-yl)-trifluorotoluene,

12% of trans-1-p-methoxyphenyl-4-propylcyclohexane

12% of trans-1-p-ethoxyphenyl-4-propylcyclohexane

10% of trans-1-p-butoxyphenyl-4-propylcyclohexane

10% of 4-ethyl-4'-(trans-4-propylcyclohexyl)-biphenyl

10% of 4-ethyl-4'-(trans-4-pentylcyclohexyl)-biphenyl

5% of 4,4'-bis-(trans-4-propylcyclohexyl)-biphenyl

5% of 4,4'-bis-(trans-4-pentylcyclohexyl)-biphenyl and

6% of4-(trans-4-pentylcyclohexyl)-4'-(trans-4-propylcyclohexyl)-biphenyl.

We claim:
 1. A nematic liquid-crystalline phase comprising at least twocomponents, wherein at least one component is a trifluorotoluenederivative selected from the following formulae: ##STR15## wherein R¹ isalkyl having 1 to 12 carbon atoms.
 2. A liquid-crystalline phaseaccording to claim 1, wherein R¹ is straight-chain alkyl having 2 to 7carbon atoms.
 3. A liquid-crystalline phase according to claim 1,wherein said at least one component is1-(trans-4-(trans-4-propylcyclohexyl)-cyclohexyl)-2-(p-trifluorotolyl)-ethane.4. In an electrooptical display element which contains aliquid-crystalline phase as a dielectric, the improvement wherein saidphase is one of claim 1.